1. Field of the Invention
The present invention relates to an apparatus for automatically fixing self-piercing nuts onto a metallic panel, wherein each nut is caused to act as a pressing punch which itself can bite into the panel lying on a caulking die so as to become integral with the panel.
2. Prior Art
A prior art apparatus for automatically fixing the so-called self-piercing nuts onto a metallic panel is disclosed for example in the Japanese Utility Model Publication No. 55-55935 corresponding to U.S. Pat. No. 4,164,072. The apparatus comprises a caulking die for supporting the metallic panel, and a press ram holding and causing a punch to face the caulking die, by means of a connecting member. The apparatus further comprises a slide guide (a nut holding block) which has a vertical bore and a nut feeding aperture extending perpendicular thereto, wherein the punch can slide up and down through the vertical bore. A flexible chute connected to the slide guide communicates with the nut feeding aperture. A guide post also incorporated in the apparatus is designed such that the slide guide can vertically be displaced relative to the connecting member between an upper limit and a lower limit. A spring is employed to urge the guide post downwardly, so that the self-piecing nut which will have entered the vertical bore through the feeding aperture is struck by the punch, whereby the nut bites or punches and is secured to the metallic panel.
Usually, the apparatus for automatically fixing the self-piercing nuts is incorporated and used in a pressing machine comprising other pressing dies or tools. The nuts are not necessarily fixed only to a plane portion of a metal panel, but sometimes are fixed to bottoms defining the bent or drawn portions of an L-shape, U-shape or the like shape. In the latter case, the punch must reciprocate a longer distance, so that the slide guide is occasionally elongated to provide a nose piece.
However, such a longer slide guide inevitably causes the punch and the guide post to make a longer vertical stroke. In a case wherein the nut fixing apparatus coexists with the other dies in the same pressing machine, the flexible chute supplying the nuts to the slide guide must be arranged not to interfere with the other dies. In consequence, such a limited layout space for the flexible chute will likely impart a twisting and/or bending stress to the slide guide and/or the guide post. Thus, the longer the vertical stroke of the post and the guide, the less smoothly they reciprocate in vertical direction.
Further, the prior art nut fixing apparatuses are designed such that each self-piecing nut is struck to a metal plate or panel when an end face of the slide guide is in a direct contact with the panel. Therefore, the slide guide sometimes interferes with the metal panel at portions thereof located proximate a bent bottom or around a recess narrower than said guide, thereby failing to fix the nut to the metal panel.